THE architect of the planned new JPMorgan Chase tower near Ground Zero left the door open yesterday to slightly reducing the size of its giant, elevated trading floors cantilevered over a new St. Nicholas Church.

“The size of the cantilever is one of those things still being studied,” Gene Kohn of the Kohn Pedersen Fox firm said of controversial images released last week.

But, he emphasized, it will still be a “cantilever of some dimension” and there’s no alternative to designing the Liberty Street building immediately south of the World Trade Center site any other way.

Kohn took polite exception to my description last week of the protruding block of trading floors facing the 9/11 memorial as a “beer belly.” (Readers likened it to a “kangaroo” or “electric chair.”)

“Things like that have a way of sticking,” he said.

I was referring to the project’s ungainly shape, which Kohn acknowledges is “unusual.” The tower will be 32,000 square feet at the base, swell to between 52,000 and 56,000 square feet from floors 12-16, and slim down above that.

The trading floors, starting at 190 feet above ground, will hover over a patch of land about two-thirds the size of a city block – an overhang like no other building in New York.

They also gesture ambiguously toward Ground Zero: Does the protrusion compatibly relate to the site’s quartet of architecturally arresting towers, or does it fight them?

Kohn noted that, at 42 stories, the JPMorgan Chase tower is much smaller than the buildings inside Ground Zero, crowned by the Freedom Tower at 1776 feet. And he defended its “preliminary” design, pointing out that the rules of the game left him no choice.

In 2004, the state, city and Port Authority agreed to rebuild the Greek Orthodox church on the northern part of the block bounded by Liberty, Greenwich, Albany and Washington streets.

The original church, destroyed on 9/11, stood on the block immediately west, where a new Liberty Park will be built.

Kohn was constrained, having to design a 1.3 million square-foot building with five trading floors of nearly 60,000 square feet each that could not be on or close to the ground.

“We were given this assignment with the church planned just north of the tower. What do you do with trading floors of this size? We can’t put them at grade, because the church is going to be there.

“So cantilevering is the only way to go. We weren’t given any other option.”

With a ceiling formed by the underside of the trading floors, Kohn saw the chance for “a great outdoor room. You’ll still see sky and daylight, like an atrium without walls on three sides” that will serve as a “a great porch facing the memorial.”

Locals feared the tower would cast shadows on the church and the new park. With no way to avoid overhanging the church, Kohn tried to turn the disadvantage into an advantage – “Here was a location suitable to its scale, where we can light it and frame it properly.”

As for the park, Kohn said, “A lot of people were concerned the cantilever would create additional shadows on it.” But, he said, extensive studies of the sun’s path year-round showed it actually won’t do that.

Kohn said his firm drew up the tower’s rough contours months ago, but held up work on such crucial issues as facade materials and detail until the bank and PA signed their $300 million deal.

Among many questions now is how to “express” the cantilevered floors, which are sloped on the north side to make them bigger as they go higher.

“For example, will they be trussed?” Kohn mused – meaning a pattern of diagonal exterior braces like those in Richard Rogers’ Tower 3.

“Given the challenge, we think we can do a wonderful piece of work, and we’re excited JPMorgan wants to be part of it.”